1. Field of the Invention
The present invention relates generally to an optical waveguide with a curved reflecting mirror surface for vertical coupling of light and a method of manufacturing the same in a practical process, which is suitable for mass production using inkjet technology.
2. Description of the Related Art
In general, the electrical connections between circuit boards, chips or systems are implemented using a metallic wire. However, as the capacity of information is getting larger and transmission speed dramatically increases, electrical problems such as skew in clock signals and electromagnetic interference (EMI) restrict speed of today's electronic systems to the limit of a few GHz.
Furthermore, thermal dissipation is another serious problem in high speed electronic systems. To overcome such problems, optical interconnection is introduced into circuit board level. Optical interconnection has great advantage over electronic wiring, not causing any EMI and thermal problems. However, vertical coupling of light on circuit board is a great challenge in routing optical signals, on the basis that most of opto-electronic components are packaged as a form of surface-mounted device.
Recently, optical coupling technologies using an optical transceiver (transmitter/receiver) module has been developed. There has been typical three vertical coupling ways known to those skilled in the art: first, directly coupling an photo-detecting device to a ribbon optical fiber or a multi-channel optical connector with a reflecting mirror inclined at an angle of 45°; secondly, coupling optical transceiver devices to a polymer optical waveguide with a reflecting mirror, which is cut at an angle of 45°; lastly, a method of perpendicularly integrating optical transceiver devices, which are packaged in a single module, with a multi-channel optical connector.
In the above cases, a Vertical Cavity Surface Emitting Laser (VCSEL) array is commonly used as a light source, while a photodiode array is used as a photo-detector.
Various optical interconnection modules for vertical coupling of light into an optical waveguide have been developed.
For example, an optical module disclosed in Korean Patent Application No. 2000-7003642 is designed in such a way that light emitted from a VCSEL is reflected through 90° at the end portion of optical waveguide and is transmitted to an optical fiber, which is connected to an optical connector, along a core formed in a substrate.
Meanwhile, Korean Unexamined Patent Publication 2003-94712 discloses a parallel optical interconnection transceiver module including an optical waveguide with a lens-type reflecting surface. This structure has advantage in reducing coupling loss caused by misalignment between optical components at coupling stage.
FIG. 1 shows the structure of the optical waveguide 40 having the curved reflecting surface that is disclosed in Korean Unexamined Patent Publication No. 2003-94712.
Referring to FIG. 1, a curved reflecting surface 44 has a predetermined curvature, which is formed at an end of the core 42 of the optical waveguide 40.
The core 42 is made of polymer or epoxy-based material transparent to specified wavelength range. The reflectance of light incident at the reflecting surface 44 strongly depends on the shape of it. To increase reflectance, reflecting surface 44 is circularly rounded with predetermined curvature.
Many methods of forming a mirror surface for vertical coupling have been proposed.
For example, 45 degree mirror surface can be fabricated by polishing the surface after cutting with a 90 degrees diamond dicing saw or a microtome blade.
Unlike the process of manufacturing the 45 degree mirror surface, the circular mirror surface shown in FIG. 1 is manufactured using an X-ray lithography process. The X-ray lithography can shape various types of objects that have 3-dimensional structure. But it needs relatively long processing time as well as expensive equipment such as a particle accelerator, which is not suitable for mass production at economical cost.